Coded track circuit signaling system



L. GIRARDIN CODED TRACK CIRCUIT SIGNALING SYSTEM A ril 14, 1942.

Filed Jan. 25, 1940 4 Sheets-Sheet l Mariel kw';&w

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Enerqg nwgzNToR Zola! PaPdm BY MS ATTORNEY L, GIRARDIN GODED TRACK CIRCUIT SIGNALQJLNG SYSTEM April 14, 1942.

Filed Jan. 25, 1940 4 Sheets-Sheet 2 INVE'NTOR' aural/2.

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April 14,1942. 1.. GIRARDIN CODED TRACK CIRCUIT SIGNALING SYSTEM 4 She ets-Shet '5 Filed Jan. 25, 1940 INVENTOR I loam, I m dzzz.

HIS ATTORNEY L. GIRARDIN GODED TRACK CIRCUIT SIGNALING SYSTEM April 14, 1942,

4 Sheets-Sheet 4 Filed Jan. 25, 1940 .INVE NTOR N lam; ardm.

5Z5 ATTORNEY coded trackcircuit class. t

r Patented Apr. 14, 1942 UNITED oonnn'ritAoK oinoorr SIGNALING SYSTEM Louis. .Gir'ardin, Paris France, assignor, by mesne assignments, to The Union Switch & Signal Pennsylvania a corporation of Application January 25, 1940', Serial No. 315,553

- .cIn France April 15, 1939 12* cam; (.01. 246-34) ,1

This invention relates to track circuitsignalins systems for railways and the :like offithe 'kind in which the track rails are sub-divided lintoiin sulated block sections to which coded signaling currents are supplied to control theoperation F of signals on thetrack or trainorhboth in. zaccordance'with traflic conditions.

The broad object of thisinventionisto reduce the power requirements and' increasexthe utility of railway signaling systems of the just defined A more specific object is to provide improved I 'facilities or approach controllingcvarious functions of coded track circuitsignaling systems without the aid ofline wires between. signal 10- cations.

"Other objects are to utilize lthesewirnproved approach control facilitiesfor the purposes of; (1) economizing trackwayv and other signaling system energy; and (2) extending the distance over which the approach of a train maybedetecteclby energy that circuit signaling system which coded signaling currents are supplied to the currents are rendered operative only upon the approach ofia train orfvehicle; That approach,

iurtherniore, is arranged to be indicated asf ar as three block sections ahead of thelloncoming train so that, for example, the approach of a h train or vehicle 1101a, level crossing, track diverga v ence or station may be detected withinia three.- 1'

block range without involving the provision of any additional control circuits;

According to the principal feature of the in yention, each of the track. sections is prouided ,with two approach detector relays arranged at the exit end of the section and adapted to be energised" respectively by alternating and direct signaling currents supplied to the track at the entrance end of the section in accordaneeflwith traffic conditions, these relays being, arranged,

in accordance with their relative cenditions of operation under the action of thejjtrack signaling currents, to control the operation of the code I transmitting, and receiving apparatusupon the approach of a train or vehicle so asflto give the 2 required signal indications anda1so',;ii desired, to effect the, indication at the desired point of the approach of the train or vehicle,

The invention is illustrated by way-ofeiiam ple in the accompanying drawingsof'whioh Fig track circuits and the devices responsiveto these ure iis-afdiagrammatic view of a single track section illustrating the principal feature of the invention. Fig. 1a represents the different forms ofen'ergy which at Various times are transmitted by'the track-circuit of Fig. 1. Figures 2, 2a and 3, when placed end to end with Figure 2 on the left and Figure 3 on the right, constitute a diagrammatic view of a number of successive track sections provided-with signaling apparatus arranged in accordance with one form of the invention, one of the track sections being shown asincluding a level or highway crossing. Figure 4 is a chart showing the operative conditions of certain relays of the system of Figures 2 and3 as a train or vehicle proceeds through thetrack sections in succession. Figure 5 is a detail view showing, in a simplified form, the connections for controlling the operationof a level or highway crossing indicator.

. In the several views of the drawingslike reference characters designate corresponding parts. Referring first to the composite diagram of Figs. 2i- 2a-3 the improvements of this invention are there disclosed in association with a coded track circuit system of automatic block signaling for a stretch of" railway track over which it will be assumed that traffic moves in the singe direction indicated b the. arrows, or from left to right in the diagram. The protected stretcher this track is divided. into the customary block sections VI,

V2,, V3, etc., by insulated rail joints and the rails of each section form a part ofa new and improved track circuit combinationv which is most clearly shown in Fig, 1 and which will be described presently.

Installed at the entrance end of each of the block'sectionsV of Figs. 2'2a--3 is a wayside the users of the highway whenever a train approaches.

Automatic block system of coded track circuit signaling 'The just named wayside signals S form a part of the codedtrack circuit system of automatic block signaling that was previously mentioned. Further included in that system are code following track relays TR installed at the entrance ends of the several track sections and operated by energy received from the rails thereof; master track batteries TB installed at the exit ends of the sections for the purpose of supplying the rails thereof with the relay operating energy just referred to; similarly located coding devices CR which code this operating energy by periodically interrupting the master rail supply circuit;

code transmitters CT which operate each of the. exit end devices CR at one or .another of the,

usual plurality of distinctive code rates; and de-' coding relays H and J at each signal location which are controlled by the track relay TR that is there installed.

In the illustrative form represented the coded system of automatic block signaling is of the three-indication variety; it is operated by 180 and 75 pulse per minute master signal control codes that selectively are supplied to the track. rails at the exit end of each section; and it requires no line wires between signal locations. In it each set of decoding relays H and J performs the usual functions of: (l) governingthe indication of the signal S at the relay location; and (2) selecting the coding of the master signal control energy which is supplied to the section to the rear. In the arrangement shown the first of these functions is effected by contacts 2| and 34 of relays H and J while the second is effected by a contact I! ofrelay H.

At'each supply location the above named master signal control codes of 180 and 75 pulses per minute'respectively are produced by contacts I80 and I5 of the code transmitters CTIBO and CT'I5. The energy pulsesof'both of those master codes originate in battery TB and they are supplied to the track rails over a connection which includes a contact I of code repeating device CR. Under the driving influence of one or the other of the code transmitter contacts I80 and I5, repeating device CR so operates this contact I that it spacesfthe recurring pulses of signal code energy in-thes'ubstantially equal on and off period manner represented at master TBCR code in Fig. la. y r

In following one or the other of these two master signal control codes the track relay TR at eaoh'of the signal locations controls the decoding; relays H and J' in customary manner. These two relays respectively are home and distant? devices and they receive pick-up energyfrom transformers Tl and TZ. These transformers, in turn are excited from a suitable source of direct current which is designated by the terminals B and C. Included in the exciting circuit of each is a pole changing contact 36 offthe controllin track relay TR. The home decoding relay H is adapted to- "of lrelay TR.

The distant decoding relay J receives its pick-up energy through a rectifier 21 from the secondary of transformer T2. That transformer,

in turn, passes energy of an intensity sufficient to pick uptherelay only when the code following relay TR responds to operating energy of the ,180 pulse'per minute code.

At each of the signal locations in the system, therefore, the 'elements just named cooperate to cause both the home relay H and the distant relay J to pick up when the track relay TR is following code at the 180 pulse per minute rate; to allow only the home relay H to pick up when the track relay responds to the slower '75 pulse per minute code; and to cause both of the relays H and J to release when the track relay TR ceases to follow code.

..,,In determining the indication which is displayed by the controlled wayside signal S, the

just described decoding relays H and J make use of the previously named contacts 2| and 34. Further included in the lamp lighting circuits of which these contacts form a part is a local enlighting intensity can be transmitted to the signal lamps G, Y and R only when relay AR is released.

When,' under that condition, the track relay TR is responding to 180 pulse per minute code andboth of the decoding relays H and J are picked up, the clear lamp G is lighted over back contact'8, front contact 2|, the winding 40 of a relay KL (later to be described) and front contact 34; when thetrack relay is responding to 75 pulse per minute .code and decoding relay H only is picked up, the approach lamp Y then receives lighting current over back contact 8, front contact 2|, winding 40 and back contact 34; and when the track relay TR fails to follow code and decoding relays Hand J are both released, the"stop lamp R is lighted over back contact 8 and back contact 2| In selecting the coding of the master signal control energy which is supplied to the track section to the rear, each of the decoding relays H (contact [1) is aided by a contact I8 of the just named relay KL at the same location. For purposes of preliminary analysis it may be assumed that this contact I8 stays picked up as shown.

When, under that condition, the track relay TR is responding to coded energy at either the 180 or the 75 pulse per minute rate and decoding relay H is picked up, the repeating device CR which codes the signal control energy for the rear track section is driven by contact I of transmitter CTIBII over a circuit that includes front contacts I1 and I8. When, however, the track relay TR fails to follow code and decoding relay H is released, the driving circuit for coding device CR is transferred by contact I'I (back point thereof) to the contact I5 of code transmitter CT'I5 and the rear track section then receives the 75 (instead of the pulse per minute signal control code.

The apparatus so far described (with the exception of the relays AR and KL) is that which ordinarily is included in a conventional frequency-code system of automatic block signaling.

Under vacant conditions of the protected stretch such a. conventional system sets all of the controlled wayside signals S at clear and supplies the rails of each section with master signal code energy at the 180 pulse per minute rate. When, however, a train enters the stretch (fromthe left in Figs. 22a--3) and advances past signals SI, S2, S3, etc., it successively deenergizes the track relays TR at those locations and thus successively conditions: (1) each of the named signals SI, S2, S3, etc., to show stop;

(2) each associated coding device CR and track I up whenever current (from source IB-C) transformers TI and T2.

battery TB tosupply the railsof the section to the-rear with energy of the 75 pulse per minute code; and (3) the first and second signals behind each stop displaying device toshow 'approach and clear.

Approach eneryization of signals 8, decodin gre- "lays H-J, and coding devices CI -CR The previously mentioned "approach-control relays AR form a part of ankapproach energizing scheme which reduces the power consumption of the controlled traffic governing apparatus by maintaining the signals S, the decoding relays of the just mentioned approach-detector relays H-J andthe coding devices CT.CR cleenergi zed at all :times except when an approaching train requires that these several devices be brought into action to provide it with a signal indication.

This. approach-energizing scheme also includes a pair of approach-detector relays KRX and KRD Whichare provided at each location and which will be more completely described present-' lya' Through the medium of contacts 19 and .20,

those approach-detector relays govern the energization .of the approach control relay AR at the same :location. Whenever either one; of the relayslKRXand KRD is pickedup, relay AR receives energizing current from sourceBCover the front point of contact l9 or 20 and by that current is held picked up. When, however, both of the relays KRXand KRD are released, the

just named energizing circuit is broken and relay AR then releases.

When picked up, each relay AR keeps the lamps I contact 2| and winding but not by way of contact 33 and winding 39.

The signal location relays KL perform lightout protecting functions later to be described and they do this through the medium of the before named contacts l8. For reasons later to be made evident each of these relays is designed to pick is passed through either of the two windings 39 and 40 thereof and to release only when those windings become deenergized. l i

'In order that the decoding relays H and, J at each location will be supplied with energizing current only when a train'approaches, the-pickup transformers TI and T2 therefor are at proper times disconnected from their exciting source BC by contacts 5 and 9of the before named approach detector relays KRX andKRLD.

both of KRX .and'iKRD. .Whenever relay KRD is released or whenever relay KRX is picked up, the code-producing devices CT+CR are connected (over contact 6 or 'I) with their energizing source and they then operate innormal manner. When, however, relay KRD is picked up at a time when relay KRX is released, the mentioned disconnection occurs at contacts 6 and 1 and devices CTCR are then rendered inactive.

, The novel track circuit combination of Fig. 1

Serving to determine the positions of the two approaching-detecting relays KRX and KRD at each signal location are. rearwardly extending track circuit facilities of the novel character most clearly represented by ,Fig. 1. There a single track section DE is shown as being equipped with the same trackway apparatus as is each of the signal blocks V2, V3and V5 of the complete system of Figs. 2-2a-3.

Comprised by this apparatus are: (1) at the section exit end E the previously named source of master signal codeenergy T3, the coding device CR, and the approach-detector relay KRX and KRD; and (2) at the .section entrance end D the previously named code following track relay TR, a source of direct current trackway energy AB, a source of alternating current trackway energy ALT, and aconnection reverser relay PC. I

The two exit end approach-detector relays KRD and KRX respectively are operated by and only by direct current energy from entrance end source AB and by alternating current energy from en,-

trance end source Alt. The direct current relay KRD thus is unresponsive to alternating current energy, It is connected withthe section rails over the back point of a contact 4 of coding device CR when that device is at rest and also during the off periods of the master signal control code which contact I of the same device at times produces. cuited over the front point of contact 4 during each rail connection separating interval and it has a release delay which is sufficient to span those intervals as long as they do not substantially exceed code period duration.

The alternating current approach-detector relay KRX is continuously connected with the sec-- tion rails over a rectifier K and a resonant unit TI. That unit includes a combined inductance and condenser circuit which freely passes a1- ternating current energy having the frequency ofentrance end source Alt, but which excludes from the relay all direct current energy from both of the sources AB and TB. v

Alternating current source Alt. may conveniently take the form of a tuned alternator which when excited by directcurrent generates a commercial frequency (as cycles per second) alternating current output voltage having the character represented at Alt. energy in Fig. 1a. In the arrangement shown this output voltage V is transmitted to the section rails through a other is pickedup, the mentioned disconnection occurs and exciting current thenis removed from For thepurpose of bringing the code produce fingdevices CT--CR at each location into action *only when a train approaches, the driving circuits "thereforare atproper times disconnected from their. energizing source BC by contacts 6 and 1 transformer TT and a resistance R. It is prorelay KRX continuously picked up as long as the supply thereof to the section rails continues.

In order that the signaling system track relay TR will not be falselypicked up by the just described alternating current energy from source This relay KRLD is short cirof? relatively high resistance.

Alt.'', it.is' designed to respond to and only to unidirectional energizing current from. one" or the other o'fdirect current sources TB andAB.

Direct current source AB may take the form of a battery which is similar to but preferably of lesser voltage than exit end battery TB. Connection of this source AB with the section rails occurs only when contacts 2 and 3 of the reverser relay PC are released. Under that condition battery AB energizes the rails over a circuit extending from the positive terminal of that battery through back contact 3 of device PC, the winding of track relay TR, impedance I, back contact 2 of device PC, conductors 45 and 44, the

section rails, and conductor 41 back to the negative terminal of battery AB.

When the track section DE is vacant the rails thereof are thus maintained by battery AB at a steady difference of potential, such as is represented at AB energy in Fig. la. At the secof coding device CR, and conductors 50 and 48 back to the other section rail. 2

As a result of this energization relay KRD is held continuously picked up both when the coding device contact 4 is following code and when that contact is continuously released.

Under the latter condition the relay winding current has the uninterrupted character indicated at AB energy in Fig. 1a Under. the former the relay winding current is interrupted during each on period of the masterTB-CR code of Fig. 1a and thus is given the pulsed character indicated at ABTB,en'ergy in Fig. 1a. Because of its slow releasing design, however, relay KRD stays continuously picked up when energized in this recurring pulse manner.

The connection reverser: relay PC of the novel Fig. l combination has two windings 5| and 52 At proper times these windings are energized over circuits which the composite diagram of Figs. 2-2a3 shows (ateach of the signal locations therein) as including contacts 6 and I of detector relays KRX and KRD and the lamps G and Y of the wayside signal S. This energization originates in source B and it occurs only when contacts 6 and I are both picked up. Under that condition winding receives current which flows to source terminal C through the filament of signal lamp G and winding 52 receives current which reaches terminal C through the filament of lamp Y. 1

These PC relay windings 5| and 52 are preferably so designed that the current drawn by each is insufficient to illuminate the series connected, signal lamp and that simultaneous energization of both is required to pick up the relay contacts 2 and 3. Those contacts, of course, are released (as shown in Fig. 1) as long as the windings 5| and 52'remain'deenergized.

When picked up,'however, the just named contacts 2 and 3 of the entrance end relay PC connect the track relay TR directly across the rails through an impedance I; when released the same contacts reverse the track relay connection and additionally include therein the direct current source AB. When so included source AB impresses upon the track rails the before described steady potential. This potential polarizes therails in the same relative manner as does that of the exit end battery TB.

Because of this relation, the track relay TR follows the coding action of contact I of exit end device CR when the reverser relay PC is released as well as when that relay is'picked up. Under the latter condition, of course, each on period pulse of master signal control code (see the master TB-CR,code portion of Fig, 1a) energy from the exit end battery TB that is transmitted to location D picks up' track relay TR 'over a circuit extending from the positive terminal of battery TB through an impedance 42, conductor 43, one of the track rails, conductors 44 and 45, front contact 3 of device PC, the winding of relay TR, impedance 1, front contact 2 of device PC, conductors 46 and 41, the other track rail, conductor 48, front contact I of device CR, conductor 49 and a resist ance R back to the negative terminal of battery TB- Under the former condition (device PC released) the entrance end received pulses of m'as tercode energy (from battery TB) also cause the track relay-TR to follow the master energy coding. Now, however, the pick-up current for relay TR is supplied by entrance end battery AB and the releases of relay TR are produced by the neutralizing or series-opposing pulses of signal code energy from exit end battery TB.

This AB-supplied pick-up current reaches the track relay TRover a circuit previously traced as extending from the positive terminal of battery AB through back contact 3 of device PC, the winding of relay TR, impedance I, back con- ,tact 2 of device PC, conductors 45 and 44, the

track rails (together with apparatusat the. section exit end), and conductor 4'! back to'the negative terminal of battery AB.

During each off period of the master signal control code the current (see AB-TB energy portion of Fig. la) flowing from battery AB into the section rails picks up the track relay TR and there holds it until the succeeding on period pulse of signal code energy is received from battery TB. Upon that reception the potential between the rails is maintained by battery TB and in consequence the drain on battery AB is interrupted. Now deprived of pick-up current, relay TR releases and there stays until the succeeding signal code off period when the resumed current drain on battery AB again picks it up.

' It will accordingly be seen that when the track section DE is vacant and the reverser relay PC is released the track relay TR picks up in step with the off periods of the entrance end received master TB-CR code, and releases in step with the on periods of that code. When, however, the exit end' coding device CR is continuously released or when section DE becomes occupied the represented re- Operation of the complete systems of Figs.

As already pointed out, the complete system of Figs, 2-2a3 provides, each of the signal blocks V therein with track circuit facilities which are a duplicate of those just described for section DE of Fig. 1. In operation of that complete system those facilities cooperate with each other and with the remaining trackway apalso maintained deenergized.

track batteries TB and the control sources .B:C) will-be seen, to be, completely free from drain. l

transformers TI actionycontact "I now connects coding devices paratus illustrated in beexplaincd. 3 I l 3 As long as all of the represented signal'jblocks V remain vacant, the equipment. for each of those blocks has the condition: which is shown forsection V5 of Fig. 3. Under thatcondition:

a manner which will now (1') at the section entrance end thefireverser relay PCis disconnected (at contact 6) from its pick-up source and hence is releasedythe track relay TR receives from battery AB steady energy l which holds it continuously picked up, and the alternator Alt. is disconnected (at contacts 5 and 9) from its exciting source and hence is inactive; and (2) 'at the section exit end the detector relay KRD receives (over the rails) 11 from entrance end, battery AB steady energy which holds it picked up, the detector relay ,KRX receives no alternating current energy and hence is released, the coding device CR (along with its transmitters 'CT) is disconnected (at contacts 6 and 1) from its operatingsource and hence also stays released, and the master track battery TBis disconnected (at contact, I.) from the section rails. i

In consequence each of the approach-control relays AR is energized (over contact and thereby held picked upr. each of the wayside signals S is disconnected (at contact,8 from its lighting source and. hence maintained deener--v gized, each set ,Of decoding relays H-J. is disconnected (at contacts 9 and 5),from its pickup source and hence kept deenergized; and each set of coding devices C'ICR is disconnected (at contacts! and 6) from its operating source and Under, the just discussed unoccupied conditions of the signalled stretch, therefore, the only energy sources inthe system that are subject to power drain arethe entrance; end track bat,-

teries AB. Those batteries are, as already r pointed out, connected with the rails of the several sections for the purpose of holding the exit end detector relays KRD therefor picked up. All other energy sources (including the exit end Now. let it be. assumed that a train vehicle traveling, from left. to, right enters the stretch by way of section V! of Fig. 2. In that figure {5b such a vehicle is represented at M. In shunting the rails of section VI vehicle M producesthe following actions. 1

At the location of signal S2 this shunt of block Vl deenergizes and releases detector relay KRDI. Thus released, contact 9 ofthatrelay' nowconditions decoding relays HI and J l for response to track relay ,TRI (.by connecting and T2 with their exciting source) and also brings alternator ALTI into CT.l--CRI- with their energizing source; and contact 20 now releases approach relay ARI.

This latter release sets up (over back contact. 8) the lighting circuits for signal S2. Reverser relay POI remains released because ofthe break in its pick-up circuit at contact 1. Under these conditions battery ABI supplies (overback contactsz and 3 of device PCI) the rails of signal block V2 with direct currentenergy and alter- I nator ALT! supplies (through transformer TT) thesame rails with alterriatingcurrent energy.

At the location of signal Sit-these two forms of energy i'espectively continue detector relay KRDZ picked up (over back contact 4 of device 75,

CR2) and shift detector relay KRXZ from its released to its picked upposltion. As aresult of this shift contact 5 of device KRX2 nowconditions decoding relays HZ and J2 for response to track relay TR2 and also brings alternator ALT2 into action; and contact} now connects coding devices,CT.2---CR2 with their energizing, source and, also picks. up 'reverser relay, P02.

This pickeup of relay PCIdisconnects (at con- 7 tacts 2 and 3) battery ABZ fromthe rails of signal block V3 and'connects track relay.TR,2,di-

rectly across those rails. Under the just stated conditions the block V3 rails receive only alternating current energy (from source ALT2) at the block entranceend. I

At. the location of signals l this alternating current energy shifts detector relayKRX3 from its released to its picked up position. At the same time the absence of rail-transmitted direct current energy at that point allows detector relay KRD3 to release. As a result of these two actions contacts 5 and 9 continue devices ALT3 and H3-J3 in their previously deenergized conditions; and contacts 6 and I continue reverser relay, P03 released but now connect coding de- Vices CT.3,-CR3 with their" energizing "source.

In consequence of the continued release of [relayPC3 and the deenergization of device ALT3, the rails of the forwardly extending block V4",- V4 which signal S4 guards now receive only direct current energy from entrance,end source A583, and they thushave the normal or vacant track condition which already has been described by reference to block V5 of Fig. 3. This same, condition, moreover, is shared bys cceeding. blocks of vacant track still further ahead.

lcircuitzjwhich includes back contact l8 of, relay At the entrance end of blockIVfl (location of isignal S3) the code following track relay: .TRZ

receives the pulses (see master TB-Clt code? portion of, Fig-la) of this '15 code. signal control fenergy byway of front contacts 2 and 3 of device PC2. In picking up and releasing instep with: those'received pulses, this track relay TR2 picks iup the home? decoding relay H2 (but produces noresponse on the part of the distant relayJD. Relay H2, in turn, completes (at front contact 33) a pick-up circuit for relay KL2. dcvic'es H2 andKLZ- establish (over their front points) a circuit over which code repeating relay CR2 is driven by contact of code transmitter CTI80.2. 2

At thelocation of signal in consequence,

the rails of'therearwardly extending, block V2 now are supplied with signal control energy coded at the 180 pulse per minute rate." This fene'rgyis derived from master'track battery TBZ attlie blo'ckexit and the recurring pulses there i of are transmitted to the railsover frontcontact I of coding device CR2.

At the entrance of block V2 (location of sig- Now, accordingly, contacts l'luand 1 8 of sections which the train is about to enter. action will be most readily understood through nal S2) the track relay TRI nowfollows the coding of this'180 pulse per minute signal-control energy which is-there received. Duringthis action, however, each on period. of-the received signal-control code produces a release-on the part of track relay TRI (due to its serial connection with battery ABI over backcontacts 2 and 3.of device PCI) and each off period of that code allows current from battery ABI to pickthe track relay up. (For further explanation see the earlier description of the TB-AB energy'portion-of Fig. la.)

In thus responding to the 180 pulse per minute signal control code of block V2, track relay TRI causes the pick-up of both of the decoding re- -lays HI and J I. Contacts 2I and 34 thereof now completethe lighting circuit for lamp G of signal S2 and cause that signal to display the clear indication. By that indication the enquires an indication therefrom. In the event of such V3 block occupancy, track relayTRZ at the entrance end of that shunted block would cease to follow code, decoding relay H2 would release contact I! and transfer the driving circuit for coding device CR2 from transmitter CTI8I'L2 to transmitter CT'I5.2, the rails of block V2 then would receive signal control energy coded at the 75 pulse per minute rate, track relay TRI at the blockentrance end now would follow that slower code, decoding relay J I would release contact 34, and lamp Y of signal S2 would now light to show that only the advance block V2 is vacant.

And finally, were this block V2 to be occupied,

then signal S2 would display to the approaching train M of Fig. 2 the most restrictive or stop indication. In the event of such V2 block occupancy, track relay TRI at the entrance end of that shunted block would cease to follow code,

'decoding relay HI would release contacts I1, 33 and 2|, and under the control of contact 2| lamp Rof signal S2 would now light to show that the nextblock in advance was occupied. Concurrently, of course, the signal control energy supplied to the rails of block VI would be transferred (by contact I8 of the now released relay KLI) from the 180 to the 75 pulse per minute signaled stretch of Figs. 2-2a3 brings into action such coding and other devices ahead as are needed to indicate the condition of the track This reference to Fig. 4. In that figure the arrows pointing upwards and downwards indicate the picked-up and the released conditions respectively 'of the two .detector relays KRX and KRD for each of the stretch sections VIV2V3V4 V4 when each of those-sections is successively occupied by the train vehicle M.

'ternator ALTI The showings of Fig. 4 forIthe positioning of vehicle M in block section VI have already been described in detail. Under that condition it has been seen that relays KRXI and KRDI are released, that relays KRXZ and KRDZ are picked upthat relay KRX3 is pickedup while relay 'KRD3 isrreleased, that relay KRX I is released while relay KRD-I is picked up, and that relay KRX4 likewise is released while relay KRD4 is picked up.

From Fig.4 it will be seen that advancement of the vehicleMfrom block section VI into block lanothersignalblock; and so on. Because of this parallel movement of the advance range of detector relay responses the already explained signal indications are made available to the train M during its entire travel through the signaled stretch of Figs. 2-2a.--3.

As, moreover, each block section in that stretch is vacated by the train the apparatus associated therewith restores itself to the normally inactive "condition that is described at the be ginning of this explanation on Complete system operation? In leaving section VI, for example, train M- allows steady energy from the entrance end source AB (not shown) to flow over the section rails to the exit end detector relay KRDI. In picking up that relay KRDI: (1) energizes approach relay- ARI over contact 20 and thus removes (at contact 8) lighting current from signal S2; (2) deenergizes (at contact -'I) lthe codingdevices CT.-I-CR.I for section VI; and (3) removes (at contact 9) the exciting current from decoding relays HI--JI and from alfor section V2. For each succeeding blocksection that is vacated a similar set of actions takes place. I

The various operations that .have been explained for the signal blocks (such as V2, V3 and V5) of the Figs. 2-2a--3 system which contain only one track section each also takes place in blocks wherein more than one section is included.

-'Such a multi-section block is shown in Figs. =2a-3 as being guarded'by signal S4 and as embracing a rear section V4 and a forward section At the junction of these two sections is apparatus which performs the repeating functions which are customary for out locations. It

includes 'devices KRX I KRDA CR4 TBd TRA AB I and ALT4 which have the same general characteristics and organization as do the correspondingly identified devices at each of the a contact 56 of the forward section track relay -TR4 the driving circuit of which contact 56 forms a part is rendered effective only when the rear section detector relay KRIX I picks up a contact 51 or whenthe rear section detector re- -lay 'KRD4 releases a contact 58; the forward section alternator ALT4 is brought into operation only when the rear section detector relay ,KRXl

.picks up a secondcontact 59 and the contacts :2 and.- 3 which control the connection of the forward section rails with direct current source AB4 and with track relay 'IR I are'carried by section;

1 mitter CTIBIM C'IJ 5.l. In. consequence, the pulses of signal conof by a connection reverser relay PC as at the signal locations-)1: I

Byvirtue ofthesspecial cut location arrangements: (1) coded signal control? energy received from the forward section is repeated (by devices TR, C'R l and TB i into the rails of the rear (2) direct current approach control energy received from the rear section isrepeated (by devices KRDAP, and AB") into the rails of the forward section; and (3)alternating current approach control energy received from therear section also is repeated (by devices KRXA and ALT4 intothe rails of the forward section.

Under vacanttrack conditions, in consequence,

occupiedby a forwardly moving train, likewise,

this two-section signal block V4 -V4 also func- .tions. in a 'manner which is fully equivalent to that of the single section blocks and whichpermits the before explained complete system actions totake place in the desired way.

The complete signalingwsystem of, the. herein disclosed invention is further so organized that each of the signallocation relaysKLperiorms alight-out protection function which will now be explained byreference to device KL! at the location of signal S2 of Fig. 2. i

Y Under the conditions which are there representedlfor signal S2, the clear lamp G thereof is lighted. Should, now the filamentof that lamp burn out, flow of current (over back contact 8, lfront contact: 211 andfront contact 34) through winding 400i relay KLI would cease and that relay: would release contact [8. That release, in

turn, would transfer the driving connectionfof coding. device CRl-i from contact I80 of transto contact 15' oftransmitter trol code energysupplied to the rearwardly extending sectionVl then would be slowed to the lower or caution rate of 75 per minute.

- Were, moreover, the lamp Y ofsignal S2 to be lighted (as a resultof contact .34 of'decoding relayJl being released) instead of lamp G, a similar set of actions would results-That is, relay KLI. would release and slowto thecaution or 75 1 rate the pulses of signal control energy then suppliedto the rails of section VI v i Non-Zine-wz're approach detection 'ove r three sigi nal blocks As the track circuit diagram of Fig. 1 shows I and as the foregoing system operation description has, brought out, the normal or vacant-track position of each set-10f the exit-end detector relays KRX-KRD is relay KRX released and relay as far ahead ,as the exit end .of block V4"-V4; that occupation of block V3 is indicated by' the detectorrelays as far ahead as the exit end of blockV5;.and so on;

Itwill accordingly be evident that each train which is within the signaled stretch of Figs.

2?2,a 3 is at .alltimes registered by the detector 3 relays KRX -KRD at the exit: end of z. (1) the signal block? which the. train. directly: occupies;

proached or occupied by a train.

comes occupiedby'a train as shown at M (2) the first vacant-block immediately in advance of the occupied block; and (3) the succeeding or second vacant block ahead.

By taking proper advantage of these detector relay registrations it at once becomes possibleto detect the approach of a train as far in advance thereof as three full signal blocks. As will become more evident presently, this extended-range detection is effected solely through: the medium of energy that is transmitted through the track rails and hence it reguires no line-wire control circuits of any kind.

Various ways of registering changes in contact position of thedetector relays KRX-KRD can, of course, be arranged. Onewhich proves very satisfactory is shownin Fig. 5. There an indication relay AN. is controlled by detector relays KRX and KRD throughthe medium of contacts 23 and 24 thereof. As long as both of the detector relays have their normal or vacant-track condition (whereinrelay; KRX is released and relay KRD is picked up), this indication relay AN is energized over the represented serial connection of back contact 23 of relayKRX with front contact 24 of relay KRD and thereby held picked up. When, however, relay KRD releases or relay KRX picks up, the just named connection is broken and the indication relay AN then releases. The change in fdetector relay contact position by which such a release is produced may, of

course, be further indicated by a signaling device of any suitable character. In Fig. 5 one such device is shown at SPN as being controlled by a contact 25 of relay AN. As long'as that relay stays picked up, this signaling device SPN is kept deenergized and hence inactive. When, however, relay AN releases, contact 25 thereof completes the energizing circuit for signaling device SPN and thus brings that device into action.

Inthe complete system of Figs. 22a-3 this just described combination of Fig. 5 is utilized to govern the highway crossing signals SPN of Fig. 3. As previously stated, the function of those signals is to warn the users of highway PN Whenever the intersected track section V4 is being ap- As long assi'gnal blocks V2, V3 and Ve V4 all remain vacant, the'crossing signals SPN of Fig. 3

front contact 24 of detector relay KRDd. Such a condition is represented by Figs. 2-2a3 and byFig. 5. Itpersists even when block VI bein the upper portion of Fig.4.

i From the time, however, thatthe train M first advances into the entrance endof block V2 until it clears the exit endof section V4, the crossing signals SPN are broughtinto and kept in operation by arelease of contact 25 of relay AN 4. Reference to Fig. 4 and earlier given description will show that this release is produced in the following manner. When the train is in block V2 the release results from a pick-up of detector relay KRX4 and a release of detector relay KRlM which breaks the energizing circuit of relay AN4 at both contacts, 23 and24; when the train is in block V3 the release results from a pick-up of detector relay KRX4 which opens. the AN4 relay circuit at contact 23; and when the train is in section. V I and/or section V4 the AN4 release :results from a releaseyof detector relay KRD4 (accompanied by a release of detector relay to break the SPN energizing circuit.

Summary From the foregoing it will be seen that the invention herein disclosed has effected important improvements in signaling systems of the coded track circuit class and in apparatus for detecting the approach of trains without the aid of line wires.

In particular it has increased the utility and decreased the power requirements of automatic block signaling systems of the coded track circuit type; it has extended the distance over which the approach of a train may be detected by energy that is transmitted through the track rails; and it has effected the above through the use of apparatus of comparatively simple character and without dispensing with any of the desirable features of coded track circuit control.

As all of these improvements are primarily a function of the track circuits and apparatus which is directly associated therewith they. are relatively independent of the coding anddecoding facilities of the coded signaling systems which they may supplement and hence are usable with a wide variety of different types and forms of such facilities.

claim is: l '1. In combination, a section of railway track over which traffic moves in a given direction, a first track circuit for said section which includes a first track relay at the section entrance end and a source of direct current energy at the section exit end, a second track circuit for said section which includes a second track relay at the section exit end and a source of direct current energy at the section entrance end, apparatus which connects said entrance end source across the rails of said section in series with the winding of said first track relay and thereby allows current from said source to pass through said winding and maintain a given polarity difference of potential between said rails, other apparatus which at times is effective to connect said exit end source across said section rails in such a way as to establish between those rails a difference of potential that is of the aforesaid given polarity and that substantially discontinues the flow of said entrance end source current through th winding of said entrance end track relay and which at other times is effective to connect said exit end track relay across said rails in such a way as to impress thereon the said trackway potential that said entrance end source maintains, and trafilc governing apparatus controlled by each of said two track relays.

2; In combination, a section of railway track,

'a first track circuit for said section which includes a code following track relay at the'section entrance end and a source of direct'current energy at the section exit end, a second track'circuit for said section which includes a detector track relay at the section exit end and a source of direct current energy at the section entrance end, apparatus which connects said entrance end source across the rails of said section inseries with the winding of said code following track relay and thereby allows to pass through said winding current from said source which holds the track relay picked up and which maintains a given polarity difference of potential betweensaid rails, coding apparatus which repeatedly connects said section rails first in given polarity establishing manner with said exit end source whereby to release said code following track relay by substantially discontinuing the fiow of said entrance end source current therethrough and then directly with said detector ,track relay whereby to impress thereon the said trackway potential that said entrance end source maintains, and trafiic governing apparatus controlled by said code following and detector track relays.

3. In combination, a section of railway track, a first track circuit for said section which includes a code following track relay at the section entrance end and a source of direct current energy at the section exit end, a second track circuit for said section which includes a detector track relay at the section exit end and a source of direct current energy at the section entrance end, apparatus which connects said entrance end source across the rails of said section in series with the winding of said code following track relay and thereby allows to pass through said winding current from said source ,which holds the track relay picked up and which maintains a difference of potential between said rails, a coding device which at times repeatedly connects said section rails first with said exit end source in such rail polarizing manner as to release said code following track relay by substantially discontinuing the flow of said entrance .end source current therethrough and then with said detector relay whereby to impress thereon the said trackway potential that said entrance end source maintains and which at other times establishes said rail-to-detector relay connection uninterruptedl thereby causing said entrance end source then continuously to energize said code following and detector track relays in series, traffic governing apparatus controlled by cludes a first track relay at the section entrance end and a source of direct current energy at the section exit end, a second track circuit for said section which includes a second track relay at the section exit end and a source of direct current energy at the section entrance end, exit end apparatus which at times connects the rails of saidsection with said exit end source in such manner thata' given polarity difierence of po-. 'tential is established between those rails and which at other times connects said rails in energy supplying relation with said second track ,trackway,potentialtthat said exit end source establishes and which at other times connects said-rails across said entranceend source through said first-track relaywinding in such series mantr erthat, current of relay pick-up intensity is upassed by said entrance' end source to saidlrails through said series connected winding when and 1 only when said given polarity: potential difference betweensaid rails is not beingestablishecl track relay at the .section exit end and a source of direct current energy at the section entrance end, apparatus; which at times is effective to connect said entrance. end source across the rails of said section inseries with the, winding of; said code following ,trackrelay in a manner allowing'to pass through said winding current from said source that holds the track relay picked up and thatmaintains a given polarity difference of potential between said rails and whichat q ther times is efi'ective to connect the saidcode -following track relay winding in direct energy receiving ,relation withsaid rails, a coding de -vice which-during recurring on code periods connects said sectionxrails with said exit end source-in such givenpolarity establishing man- "neras to release said code following track relay underits firststatedcondition ofserial connection and to pick up that relay underits second istated condition ofidirect connection and which during intervening fofi period intervals connects saidrails with said detector track relay whereby to impressthereon the said trackway potential that said :entrance end sourcemaintainsfland tralilic' governing {apparatus controlled by said codefollowing and} detector track relays.

i 6 In combination, a section of railway track,

a first source of. direct current energy for said section atthe exiten-d thereof, coding apparatus which connectssaid exit end source with the rails of said section in periodically interrupted manner a and thereby produces a-trackway code made up of recurringflon period pulsesof rail potential that are separated-by off period intervals, a 1 code-following track relay for said section at the entrance end thereoi,-a second source of direct current energy ior said section at the entrance end thereof, apparatuseifective at times to conl nect thewinding of said track relay directly across said section rails and thereby cause that relay to pick up and release in respective step with the on"- period pulses and the fofffi period intervals of the entrance endreceived said tra ckway code potential and efle ctiveat other "times to connect gsaid entrance end sourceacross-the section rails throughsaid tr ack elay windinginlsuch series mannerthat current offrelay pick-up intensity is passed bysaidl entrance end sour'ceithrough said winding, to said railsonlyduring the foff periods of said received tr wkway code whereby during those other times; tracklrelay releasesfand r, picks up inrespective-step with said on. and

fq ff periodsof that receivedcode.

l "7. In combination; a sectionfof railway track over; which tramc moves inagivendirection, a -first track circuit for said section which includes a source of direct current energyat the s'ection exit and anVentranceen-d codeiollowing track reenergy and that at all times follows the coding of pulsed direct current energy which said exit end source may transmit to, the section entrance, a second track circuit for said section which includes asource of direct current energy at the section entrance and a first exit end detector track relay that is unresponsive to alternating current energy and that isloperable by and only'by unidirectional energy from said entrance end direct current source,a third track circuitfor saidsection which includes a source of alternating current energy at the section entrance and a second detector track relay seine section exit that is unresponsive to direct current energy and that at all times respondsto ther received energyfromsaid alterhating current source, a coding device for at times connecting said exit end direct current source with the section rails inperiodically interrupted manner whereby under vacant track conditions to produce codeiollowing operation on the part of i said entrance end trackrelay, meansior at times connecting said entrance .endjdirect current source with said" rails whereby under vacant track conditions to pick up said first exit end detector track relay, means for at times causing said al- "ternatirig current source to supply energy tosaid rails whereby under vaoanttrack conditions to pick up said second exit end detector track retrafiic governing apparatus controlled by said first and second detector tr'ack relays and distinctively responsive toleach combination of "picked up and released positions thereof.

8. In combination: a stretchpf railway track which includes a plurality of consecutively adjoin- 40 moves in the direction of from the first to the ing track sections and through whichtrafli-c secondof said sections; a firsttrack'cirouit for each of said sections which includes a sourceof direct current energy at the section entrance and at section exit a first detector track relay that is responsive to direct current energy from said entrance endisource but not to alternating current energy; a second track circuit for each of said sections which includes a source of alternating current energy at the sectionentrance and at the seetion'exit a seconddetector track relay that is responsive to energyfrom said entrance end alternating current source but not to direct I current energy; means controlled by the said two detector track relays at the exit of each of said sections for connecting the rails of the next section in advance with the said two entrance end sources therefor in such selective manner that those rails receive direct current energy only further conditions of approaching traffic; and

traffic governing apparatus at selected of said section exit ends controlled by the said two detector track relays which are there located.

9. In combination: a stretch of railway track whichaincludes a plurality of consecutively adjoining track sectionsand through which "traffic moves in the directionof from the first to the 1 second of said sections; a first track circuit for each of said sections whichincludes a source .of

directcurrent energy at the section entrance and lay that, is unresponsive to alternating current said entrance end source but not to alternating current energy; a second track circuit for each of said sections which includes a source of alternating current energy at the section entrance and at the section exit a second; detector track relay that is responsive to energy from said entrance end alternating current source but not to direct current energy; means controlled by the said two detector track relays at the exit end of each of said sections for connecting the rails of the next section in advance with the said two entrance end sources therefor in such selective manner that those rails receive only direct current energy when the two sections immediatelyto the rear of the supply location are bothunoccupied, only alternating current energy when only the first section immediately behind the supply location is vacant, and both direct current and alternating current energy when that first rearwardly extending section is occupied; a-nd traffic governing apparatus at selected of said section exit ends controlled by the said two'detector track relays which are there 10- cated.

ratedetermined by tramc conditions in advance and at the section entrance end a code follow-. ing track relay that is unresponsive to alternating current energy and that follows the coding of the pulsed direct current energy which said exit end source at times transmits to said entrance end; a first approach-control track circuit for each of said sections which includes at the section entrance a source of direct current energy and at the section exit a first detector track relay unresponsive to alternating current energy and operable by and only by unidirectional energy from said entrance end direct current source; a second approach-control track circuit for each .of said sections which includes a source of alternating current energy at the section entrance and a second detector track relay at the section exit that is unresponsive to direct current energy and that is operable by there received energy from said alternating current source; means controlled by the said two detector track relays at the exit end of each of said sections for connecting the rails of the next section in advance with the said two entrance end sources therefor in such selective manner that those rails receive only direct current energy when. the two sections immediately to the rear of the supply location are both unoccupied, only alternating current energy when only the first section] immediately behind the supply location is vacant, and both direct current and alternating current energy when that first rearwardly extending section is occupied; and control means at the exit of each of said sections for bringing the there located said section coding apparatus into action when the there located said direct current detector track relay is released or when the there located said alternating current detector track relay is picked up whereby each train passing through the stretch initiates operation on the part of the said coded track circuit in the occupied section and in each of the two sections immediately thereahead.

11. In'combination: a stretch of railway track which includes a plurality of consecutively adjoining track sections; a coded track circuit for each of said sections which includes at the section exit end a source of directqcurrent energy together with coding apparatus that recurrently connects said'source with the section rails at a code pulse rate determined by traffic conditions in advance and "atthe section entrance end a code following track relay'that is unresponsive to alternating current energy and that follows the coding of' the pulsed direct current energy which said exit end source transmits-to said entrance end; entrance end decoding apparatus for each section which normally is deenergized and hence inactive but which when supplied with exciting energy responds distinctively to each rate at which the there" located said section track relay follows code; a first approachcontrol track circuit'for each of said sections which includes at the section entrance a source of direct current energy and at the section exit a first detector track relay operable by and only by unidirectional energy from said entrance end direct current source; a second approach-control track circuit for each or said sections which includes a source of alternating current energy at the section entrance and a second detector track relay at the section exit-operable by and only by energy there received from said alternating current source; means controlled by the said two detector track relays at the exit'end of each of said sections for connecting the rails of the nextsection in advance with the said two entrance end'sources therefor in such selective manner that those rails receive only direct current energy when the two sections immediately to the rear of supply location are both unoccupied, only" alternating current energy when only the first section immediately behind the supply location is vacant, and both direct current and alternating" current energy when that first rearwardly extending section is occupied; and control means at the exit end of each of said sections for supplying the said decoding apparatus at theentranoe of the there adjoining advance section with exciting energy when the there located said direct current detector relay is released or when the therelocated said alternating current detector track relay is picked up whereby each train that passes through the stretch causes to come into action the said decoding apparatus at the entrance end of each of the three vacantsectionslimmediately ahead of the train. 7 I

12. In combination: a stretch of railway track which includes a plurality of consecutively adjoining track sections; a coded track circuit for each of said sections which includes at the section exit end a source of direct curr ent energy together withcoding apparatus that recurrently connects said source with thesection rails at a code pulse rate determined by trafiic conditions in advance and at the section entrance end a code followingtrack relay that is unresponsive to alternating current energy and that follows the coding of the pulsed direct current energy which said"exit"'end source transmits to said entrance end; entrance end decoding apparatus for each section which normally is deenergized and henceinactive but which when supplied with exciting energy responds distinctively to each rate at which the there located 2,279,981 said section track relayfollows code; an entrance end signal for each of said sections controlled by the there located said decoding apparatus but normally maintained deenergized;

first and second approach-control track circuits for each of said sections respectively including,

an entrance end source of direct current energy together with a first exit end detector track relay operable only by energy'fr'om said direct current source and an entrance end source of alternating current energy together with a sec- 0nd exit end detector relay operable only by energyfrom said alternating current source; means controlled by the said two detector track relays at the exit end of eachof said sections for connecting the rails of the next section in advancewith the said two entrance end sources therefor in one selective manner when the track immediate rear.

the relays whereby to make indication control available to the said signals at those two advance section entrance ends; and a circuit for supplying energizing current to each of said signals whenever the said two detector track relays at the location of the signal both become released due to a train entering the section to the LOUIS GIRARDIN. 

